1. Field of the Invention
This invention relates to a semiconductor device which is formed on an amorphous or polycrystalline substrate.
2. Description of the Prior Art
By way of example, it has recently been attempted to elongate a linear photosensor array for reading a picture in a facsimile transmitter. Heretofore, silicon MOS and CCD (charge coupled device) type imaging sensors have been employed as the linear photosensor arrays. However, the sensor length is about 30 mm in the present situation, and the limitation of the sensor length which is technically realizable is approximately 125 mm. This is because the sensor length is determined by the size of a single-crystal silicon wafer which can be fabricated. Anyway, it is unavoidable to adopt a system wherein an image is scaled down with a lens optical system and then read by means of a sensor shorter than the width of an original (for example, 210 mm in the A4 format). In this case, the optical path length is as great as, for example, 200 mm, which is a major cause for hindering the miniaturization of the apparatus. Recently, to the end of miniaturizing the apparatus, the development of linear photosensor arrays of the close contact reading system has become serious. This is a system wherein a linear sensor of a length equal to the width of an original is realized by employing a thin film photodiode array of Se-As-Te chalcogenide glass, CdS or the like instead of the silicon sensor and wherein an image is read by holding the original and the sensor in close contact. This system has such merits (1) that since the lens optical system is not used, the miniaturization of the apparatus becomes possible, (2) that the adjustment of an optical system is easy, (3) that the problem of defocusing in the marginal part of a lens is not involved, and (4) that a high resolution is possible. Since, however, there is not any suitable elongate active device array, it is difficult to realize an elongate self-scanned photosensor in which a sensor portion and a scanner portion are made unitary. This fact is a serious hindrance to putting the elongate sensor of the close contact reading system into practical use. In order to realize the elongate self-scanned photosensor, the development of the elongate active device array suitable therefor is awaited.
As other examples, a liquid crystal display device and an electroluminescence display device have been developed as flat display panel to replace conventional cathode-ray tubes. There have already been made the trial manufacture of a display device combined with a thin film transistor array of CdSe or the like and the trial manufacture of a display device combined with a silicon scanner. In case of the former, there are such problems that the thin film transistor array free from defects cannot be realized and that the operating characteristics of thin film transistors are unstable. In case of the latter, since the size of the single-crystal silicon wafer which can be fabricated is limited, the maximum limit of the dimensions of the device is 75 mm.times.75 mm in the present situation, resulting in the disadvantage that the device is too small in case of considering the application to a flat TV screen. Also to the end of applying the liquid crystal display device and the electroluminescence display device to the flat TV screen, the development of a suitable active device array of of large area is awaited.